Cataracts are a major cause of blindness-in the world and the most prevalent ocular disease. Visual disability from cataracts accounts for more than 8 million physician office visits per year. When the disability from cataracts affects or alters an individual's activities of daily living, surgical lens removal with intraocular lens (IOL) implantation is the preferred method of treating the functional limitations. In the United States, about 2.5 million cataract surgical procedures are performed annually, making it the most common surgery for Americans over the age of 65. About 97 percent of cataract surgery patients receive intraocular lens implants, with the annual costs for cataract surgery and associated care in the United States being upwards of $4 billion.
A cataract is any opacity of a patient's lens, whether it is a localized opacity or a diffuse general loss of transparency. To be clinically significant, however, the cataract must cause a significant reduction in visual acuity or a functional impairment. A cataract occurs as a result of aging or secondary to hereditary factors, trauma, inflammation, metabolic or nutritional disorders, or radiation. Age related cataract conditions are the most common.
In treating a cataract, the surgeon removes the crystalline lens matrix from the lens capsule and replaces it with an intraocular lens (“IOL”) implant. The typical IOL provides a selected focal length that allows the patient to have fairly good distance vision. Since the lens can no longer accommodate, the patient typically needs glasses for reading. The surgeon selects the power of the IOL based on analysis of refractive characteristics of the patient's eye prior to the surgery. However, in a significant number of cases, after the patient's eye has healed from the cataract surgery, there is a refractive error that could not be predicted. It is quite common for residual errors after IOL implantation to occur, and in fact, such errors may occur in the vast majority of IOL patients. This error reportedly averages approximately 0.6 diopters, with a +/−0.5 standard deviation. Thus, many patients experience an error of over 1.0 diopter.
Various types of methods and apparatus have been proposed for altering the corrective power of an ophthalmic lens in-situ. For example, U.S. Pat. No. 6,450,642 to Jethmalani et al. describes a lens that is capable of post-fabrication power adjustment. Specifically, a partially polymerized polymer lens matrix is described that is capable of stimulus-induced further polymerization to permanently alter the lens in a selected shape.
U.S. Pat. No. 5,443,506 to Garabet describes a fluid-filled lens wherein the focusing power may be altered by changing the index of refraction of fluid carried within a central optic portion. U.S. Pat. No. 5,066,301 to Wiley describes an IOL having a fluid-filled or gel-filled lens that carries a plurality of light-reflective particles, wherein the orientation of the particles is controlled by an electromagnetic field to thereby alter the spherical power of the lens. In another similar approach, U.S. Pat. No. 4,787,903 to Grendahl discloses a fresnel-type IOL with an overlying layer of a liquid crystalline composition that has a variable index of refraction depending upon its stimulation by electrical or light energy to provide a post-implant adjustability.
U.S. Pat. No. 4,816,031 to Pfoff discloses an IOL with a hard PMMA lens separated by a single chamber from a flexible thin lens layer. The lens assembly is adjusted by microfluid pumps that vary a volume of fluid between the PMMA lens portion and the thin layer portion. U.S. Pat. No. 5,288,293 to O'Donnell discloses an intraocular lens comprising a plurality of layers of materials that respond to the application of laser energy to form microfenestrations that alter the anterior lens curvature.
Although previously known workers in the field of in-situ adjustable lenses have made some progress, the relative complexity of the methods and apparatus developed to date have prevented widespread commercialization of such devices. Moreover, previously known methods and apparatus have been directed to in-situ modifications that attempt to alter the lens axial position within the eye or overall curvature of the lens. However, such gross modifications to lens position or curvature are limited by materials and space constraints.
In view of the foregoing, it would be desirable to develop in-situ adjustable lenses that overcome the drawbacks of previously known devices. It would therefore be desirable to provide apparatus and methods that enable localized modification of the surface of a lens to correct errors, such as defocus error. This may be commonly thought of as moving the focus of the IOL system to the retina, and may be effected by actual axial motion and/or modification of the surface of the IOL, e.g., by changing the radius of curvature of one or more of the surfaces of the IOL.
In addition to modifying the placement of the focal point at the retina, it would be desirable to provide methods and apparatus that permit in-situ localized correction of other aberration properties of the eye, for example astigmatism of the eye, which may be associated with the cornea, or to correct higher order aberrations to improve visual acuity.
It also would be advantageous to provide methods and apparatus for manipulating the surface of an IOL on a localized basis after the IOL has been implanted and the access incision has healed. In order to provide such in-situ modification of the IOL surface, it would be desirable to provide an IOL configured to be modified by application of energy from a remote source, such as a laser, radio-frequency energy or ultrasonically.
It still further would be desirable to provide methods and apparatus for manipulating the surface of a lens in-situ, wherein the application of energy from an external source is performed in cooperation with a wavefront sensor system, so as to permit optimization of localized correction of the lens.